Currently, in accordance with the trend toward the high-speed and high density of information transfer, and requirement of consumers for high-quality products such as large screen, high-quality images, multifunction and high performance, large-sized flat panel displays (FPD) are used. In accordance with the trend toward large size and slimness of displays and an increase in demand for notebook PC, various types of flat displays such as LCDs, PDPs, Rear-projection TVs and the like are developed and commercialized. However, in the case the displays are exposed to external light such as natural light, the surface reflection light provides fatigueness to eyes of the user or causes a headache, and an image clarity that is formed in the display is not recognized as a clear image.
In order to overcome the disadvantages of the prior art, the concave and the convex are formed on the display surface to scatter external light on the surface, thereby obtaining the anti-glare effect. However, there still exists a problem wherein the image is reduced on the high resolution display. In order to overcome this disadvantage, a method of adding particles for inducing the internal scattering to the coating layer is suggested.
In order to solve the problems described above, various solutions are suggested. These suggestions will be described, disadvantages thereof will be analyzed and technologies for further improvement will be suggested.
Korean Registered Patent No. 10-046782 discloses a high resolution anti-glare coating layer that includes a first particle having an average diameter of 0.05 to 1 μm, in which a difference between refractive indices of an acrylate binder resin and the first particle is 0.2 to 0.5, and a second particle having an average diameter of 0.5 to 3 μm, in which a difference between refractive indices of an acrylate binder resin and the first particle is not more than 0.1. However, there is a disadvantage in that since a difference between refractive indices of the acrylate binder resin and the first particle is high, the contrast is reduced.
Meanwhile, Korean Registered Patent No. 10-037840 and Japanese Unexamined Patent Application Publication No. 2001-3178 disclose an anti-glare coating layer that includes at least two or more light transmissive particles in a binder resin, in which a difference between refractive indices of the light transmissive particle and the binder is 0.03 to 0.2 and the light transmissive particles have different refractive indices. However, there is a disadvantage in that the anti-glare property is reduced on the basis of the same image clarity and haze value and the contrast is reduced because of the haze of 10% or more.
In addition, Korean Registered Patent No. 10-0296369 discloses an anti-glare coating layer including a light transmissive diffusing agent in a binder resin, in which the external haze value by the concave and the convex of the surface thereof is 7 to 30, and the internal haze value by the light transmissive diffusing agent is 1 to 15. However, there is a disadvantage in that the contrast is reduced because of the high surface haze value. Japanese Unexamined Patent Application Publication No. 2002-67675 discloses an anti-glare coating layer that includes a spherical particle having a refractive index of 1.55 or more in a binder resin and an amorphous particle having a refractive index of 1.48 or less, in which the thickness of the binder resin is more than the average diameter of the spherical particle. However, there is a disadvantage in that the anti-glare property is reduced on the basis of the same image clarity and haze value.
Japanese Unexamined Patent Application Publication No. 2002-185927 discloses an anti-glare coating layer that includes an organic material particle having an average diameter of 1 to 7 μm and an inorganic material particle having an average diameter of 0.1 μm in the binder resin, in which the thickness of the binder resin is 0.3 to 3 times more than the average diameter of the organic material particle. However, since the inorganic material particle is not attached to the surface of the organic material particle, there is a problem in that the concave and the convex cannot be formed on the surface by the inorganic material particle, thus reducing the anti-glare effect because of the particles.
Japanese Registered Patent No. 3507344 discloses an anti-glare coating layer including at least one light transmissive particle in a binder resin, in which a difference between refractive indices of the light transmissive particle and the binder resin is 0.3 or less and which is protruded from the surface of the binder resin layer by 0.1 to 0.3 μm. However, there is a problem in that the anti-glare property is reduced on the basis of the same image clarity and haze value.
Korean Unexamined Patent Application Publication No. 10-2005-0006349 discloses a light absorption layer that includes metal oxide having a core-shell structure and a solar battery that is provided with the same. However, since indeterminate form metal oxide crystals having the high refractive index are used as a core and a shell consists of an amorphous or crystal metal oxide, there is a problem in that it cannot be applied to a composition for anti-glare coating.
In general, in the anti-glare coating film, the haze relates to external scattering because of roughness of the coating layer surface and internal scattering because of a filler in a binder resin, the anti-glare effect relates to external scattering because of the surface roughness, and the image clarity relates to the degree of diffusion of light. In addition, the degree of diffusion of light relates to a difference between refractive indices of the binder resin and the particle and the surface roughness of the coating layer. In particular, the image clarity is reduced as the surface of the coating layer becomes rough. Accordingly, since the image clarity and the anti-glare property are in an inverse proportion, in the production of the anti-glare coating film for high resolution display having the excellent image clarity and anti-glare property, the controlling of the surface roughness may be an important technical factor.
In the case of the known spherical particle, it is difficult to produce an anti-glare coating film having the excellent image clarity and anti-glare property, and RGB pixels are mixed with each other because of the lens effect of the particle.
In addition, generally, in the case the crosslinked organic material particles are used, a good solvent is used to perform monodispersion of the particles. However, in this case, since the crosslinked particles are swollen and the surface thereof becomes sticky, collision occurs between the particles and the particles are coagulated. Thus, there is a problem in that the storage stability of the coating composition is reduced.
As described above, in the prior art, in a flat display, an effort has been made continuously to sufficiently realize the antiglare effect and ensure the excellent image clarity.